Getting a partially framed mdframed

Question

Using mdframed we can opt out any of the four bounding lines. But what I want is, both the vertical lines will be present, but instead of top and bottom lines, I need a partial line at top-left and another partial line at bottom-right. The following is the code I have tried so far:

\documentclass{article}

\usepackage[framemethod=tikz]{mdframed}

\usepackage{lipsum}

\begin{document}

\mdfdefinestyle{myboxstyle}{%
  rightline=true,
  innerleftmargin=10,
  innerrightmargin=10,
  linecolor=gray,
  outerlinewidth=1.0mm,
  topline=false,
  rightline=true,
  bottomline=false,
  skipabove=\topsep,
  skipbelow=\topsep
}

\begin{mdframed}[style=myboxstyle]
  \lipsum[1]
\end{mdframed}

\end{document}

The above produces the following image where the lines at top and bottom are the ones I failed to get.

Answer 1

Here's a tcolorbox version. Just adjust the 2cm to your liking.

\documentclass{article}
\usepackage[skins]{tcolorbox}

\newtcolorbox{mybox}{enhanced,sharp corners=all,colback=white,colframe=gray,toprule=0pt,bottomrule=0pt,leftrule=1pt,rightrule=1pt,overlay={
    \draw[gray,line width=1pt] (frame.north west) -- ++(2cm,0pt);
    \draw[gray,line width=1pt] (frame.south east) -- ++(-2cm,0pt);
}}

\usepackage{lipsum}

\begin{document}

    \begin{mybox}
      \lipsum[2]
    \end{mybox}

\end{document}

---

Update: Title addition. To put more distance between title and text just use bottom=1pt (or more) in boxed title style.

\documentclass{article}
\usepackage[skins]{tcolorbox}

\newtcolorbox{mybox}[1]{enhanced,sharp corners=all,colback=white,colframe=gray,toprule=0pt,bottomrule=0pt,leftrule=1pt,rightrule=1pt,overlay={
    \draw[gray,line width=1pt] (frame.north west) -- ++(2cm,0pt);
    \draw[gray,line width=1pt] (frame.south east) -- ++(-2cm,0pt);
},attach boxed title to top left,boxed title style={frame hidden,interior hidden},title={\color{black}#1}}

\usepackage{lipsum}

\begin{document}

    \begin{mybox}{Test}
      \lipsum[2]
    \end{mybox}

\end{document}

Update 2: If you have a boxed title which is of only one line height you could be interested in this hack:

\documentclass{article}
\usepackage[skins]{tcolorbox}

\newtcolorbox{mybox}[1]{enhanced,sharp corners=all,colback=white,colframe=gray,toprule=0pt,bottomrule=0pt,leftrule=1pt,rightrule=1pt,overlay={
    \draw[gray,line width=1pt] (frame.north west) -- ++(2cm,0pt);
    \draw[gray,line width=1pt] (frame.south east) -- ++(-2cm,0pt);
},attach boxed title to top left={yshift=-20pt},boxed title style={frame hidden,interior hidden},top=.75cm,title={\bfseries\color{black}#1}}

\usepackage{lipsum}

\begin{document}

    \begin{mybox}{Test}
      \lipsum[2]
    \end{mybox}

\end{document}

Update 3: Here's the "correct" way to change the title height.

\documentclass{article}
\usepackage[skins]{tcolorbox}

\newtcolorbox{mybox}[1]{enhanced,sharp corners=all,colback=white,colframe=gray,toprule=0pt,bottomrule=0pt,leftrule=1pt,rightrule=1pt,overlay={
            \draw[gray,line width=1pt] (frame.north west) -- ++(2cm,0pt);
            \draw[gray,line width=1pt] (frame.south east) -- ++(-2cm,0pt);
    },
    coltitle=black,colbacktitle=white,titlerule=0pt,
    title={\vskip5pt\bfseries#1}
}

\usepackage{lipsum}

\begin{document}

    \begin{mybox}{This is a very long title which seems pretty ridiculous, but is used, although it is nonsense}
      \lipsum[2]
    \end{mybox}

\end{document}